High-transition-temperature (T.sub.c &gt;77 degrees K.) superconducting materials are more readily useable than low-transition-temperature superconducting materials over a wider range of technological applications because of simplified and lower cost cooling requirements. For example, one class of high-transition-temperature superconducting materials is based on oxide ceramic materials with one component comprising a trivalent rare earth element, such as Yttrium (Y), Lanthanum (La), Neodymium (Nd), Europium (Eu), Samarium (Sm), Gadolinium (Gd), Lutetium (Lu), and Scandium (Sc). The basic chemical representation of these ceramic materials is A-Ba-Cu-0 where A is the trivalent rare earth element. Typical stoichiometry would include ABa.sub.2 Cu.sub.3 O.sub.6+x or ABa.sub.2 Cu.sub.3 O.sub.7-x where x is a variable. These materials are extremely brittle in bulk form and are not easily formed into rods, wires, tubes or plates. The superconductive electron transport in crystalline oxide materials is confined to a crystalline plane in those materials; hence, the film microstructure must be properly aligned with the current flow through the film to achieve anisotropic superconductivity. The relative alignment of the group of crystalline grains strongly affects superconductivity in polycrystalline films; for example, it is important whether the crystallites have a random rather than an ordered distribution of orientations.
The processing of oxide ceramic materials using prior art methods was via grind-sintering fabrication, which is a very time-consuming process. It is also difficult to control the microstructure of products such as grain size and grain orientation and to fabricate thin crystalline films of these materials with the desirable crystalline plane orientation using prior art grind-sinter technology.
A thin film deposition method for oxide ceramic materials would be desirable in order to better control desired microstructure and stoichiometry of these materials. Pending application Ser. No. 903,688 cited above describes the basic apparatus and method for using reactive sputter deposition to coat HMF glass fibers with hermetic thin films. This apparatus principally employs a cylindrical magnetron. An anode is used which either extends partially or entirely along the axis of the magnetron in the form of a mesh. In addition, a coaxial extraction grid may be employed with the apparatus to provide additional ion or electron bombardment of the glass fiber during coating. This external particle bombardment provides a means to tailor the deposited thin film properties toward those physical, chemical and electrical characteristics required of hermetic coatings, such as film density and film stress. In the present invention the ternary metals A-Ba-Cu or the ternary metal ceramic oxides, such as A-Ba-Cu-0, where A is a trivalent rare earth element, are used as the materials for the magnetron cathodes, while gaseous oxygen or mixtures of oxygen and flourine are used as a reactive gas in the magnetron discharge. Other gases such as argon, krypton and nitrogen might be used in addition to oxygen. Film morphology, film stress, and microstructure characteristics such as grain size and grain orientation are better controlled by ion and electron bombardment created by the coaxial extraction grid during deposition, especially when used together with an external magnetic field. The chosen radius of the extraction grid varies its cylindrical area and hence varies the total current extracted. Control of these parameters is difficult using conventional techniques to coat cylindrical or rectangular cross section structures. Film deposition rates up to hundreds of Angstroms per second are possible using magnetron sputtering, especially when the magnetron discharge is electron beam assisted, so that high throughput of coated films of a given thickness is possible. In-situ deposition of a thin film interface layer, on either side of the ceramic oxide film, as well as the deposition of hermetic coatings is possible when using more than one magnetron apparatus operating in tandem.
In sputtering film coatings, the method described by Springer has been used, although it has not been suggested for hermetic coatings. See Robert W. Springer and C. D. Hostford, 20 Journal of Vacuum Science Technology 462-465 (1982). In the referenced method, a film of pure metal, such as aluminum, is sputter deposited using only an inert gas in the magnetron apparatus. Then, a thin film of Al.sub.x O.sub.y or Al.sub.p N.sub.q is deposited by momentarily admitting the reactive gas (oxygen or nitrogen, respectively) into the magnetron apparatus. The variable x and y designate the stoichiometry of the aluminum-oxygen compound. Similarly, p and q designate the stoichiometry of the aluminum-nitrogen compound. Idally, x=2, y=3, and p=q=1, but other stoichiometries of the films are also satisfactory. This second film may be substantially thinner than the first. In this manner, the columnar microstructure of the film is disrupted, making the film more dense. Metals other than Aluminum may be used, as long as they can be reacted in a similar manner with a gas which can be easily employed in the magnetron apparatus. Alternatively, the metal film can be made thin and the molecular film can be made thick.
Pending application Ser. No. 928,518 cited above describes the use of a line-shaped electron beam to create a melt zone on a thin film, combined with a focused magnetic field to reduce crystalline defects in the film over a wide area disc. Application Ser. No. 636,395 teaches electron beam induced zone melt recrystallization of an intermediate polycrystaline or amorphous layer sandwiched between a substrate and an encapsulation layer. The simultaneous use of electron beam heating, together with directed external magnetic fields, which has been previously taught for the reduction of defects may also be effective to both increase the size of crystallites and the narrow distribution of orientations of the crystallites in superconducting materials in one preferred direction over another. Moreover, transition may be made from amorphous to polycrystalline or from polycrystalline to crystalline films by annealing or zone melt recrystallization, respectively.
Conventional differential pumping techniques allow a cylindrical substrate at atmosphereic pressure to be introduced into and from a partial vacuum where the magnetron is located.